Once the main part of fermentation is complete (first 5-7 days) how important is it to maintain a good fermentation temperature (66-70 degrees for ale) after that point? Is it gonna affect the final product if after fermentation slows that temps get a bit over/under the recommended side hotter or colder?

If it gets lower, that could cause a high FG, as the yeasties could be put to sleep. Better for temps to be flat to slightly up, if at all possible.

Not really. He said they'd go down a "bit." If by "bit," he means a couple of degrees, then no, they are not going to go to sleep. Most ale yeasts (I don't know his strain) work well in the 60s, and the fermentation always adds a few degrees anyways for a bit of insurance.

__________________
Tried to keep up with this signature, but just couldn't.

Most of the time I would rather the temperatures be a little on the high side after fermentation completes. This helps the yeast stay active and clean up fermentation by products and attenuate the beer just a little more. An exception might be something a little sweet like a mild.

Most of the time I would rather the temperatures be a little on the high side after fermentation completes. This helps the yeast stay active and clean up fermentation by products and attenuate the beer just a little more. An exception might be something dark and sweet like a douplebock.

Really? He is at 66-70 now. After 5 days, fermentation is likely still going on. You'd prefer him to be at ~72 after 5 days than ~64? With fermentation likely still going on, the ~64 ambient is going to be more like ~69 in the fermenter, and the ~72 ambient is going to be more like ~77 in the fermenter. After 10 days or 14 days, then yes definitely, but I'm not sure ~77 is great on day 6 and thereafter. At least in my experience..

__________________
Tried to keep up with this signature, but just couldn't.

Really? He is at 66-70 now. After 5 days, fermentation is likely still going on. You'd prefer him to be at ~72 after 5 days than ~64? With fermentation likely still going on, the ~64 ambient is going to be more like ~69 in the fermenter, and the ~72 ambient is going to be more like ~77 in the fermenter. After 10 days or 14 days, then yes definitely, but I'm not sure ~77 is great on day 6 and thereafter. At least in my experience..

What I'm trying to express, albeit poorly, is two fold. First temperature fluctuation has in impact on the yeast regardless of if the change is up or down. Second whether to age the beer slightly warmer for a period of time after fermentation completes or at a lower temperature is very dependant on the situation.

You have a lot of good points. Fermentation temperature, during the exponential growth phase, is typically higher than ambient air conditions. However the exponential phase ends about the same time that the gravity of the beer stops dropping. At that point the temperature inside the fermentor will be very close to the ambient air temperature. So we are talking about rather high fermentation temperatures, but not quite as high as you have indicated.

Almost no beers will benefit from long term ageing at 72°F, but, given the choice of cooling or heating after a warm fermentation that likely produced some unwanted byproducts, I would choose a warm period for a couple of days to promote clean up (absorption of byproducts) by the yeast. However, if the beer doesn't taste to terribly green then cooling it might be the best choice.

What I'm trying to express, albeit poorly, is two fold. First temperature fluctuation has in impact on the yeast regardless of if the change is up or down. Second whether to age the beer slightly warmer for a period of time after fermentation completes or at a lower temperature is very dependant on the situation.

You have a lot of good points. Fermentation temperature, during the exponential growth phase, is typically higher than ambient air conditions. However the exponential phase ends about the same time that the gravity of the beer stops dropping. At that point the temperature inside the fermentor will be very close to the ambient air temperature. So we are talking about rather high fermentation temperatures, but not quite as high as you have indicated.

Almost no beers will benefit from long term ageing at 72°F, but, given the choice of cooling or heating after a warm fermentation that likely produced some unwanted byproducts, I would choose a warm period for a couple of days to promote clean up (absorption of byproducts) by the yeast. However, if the beer doesn't taste to terribly green then cooling it might be the best choice.

I agree with everything you said, and generally speaking, it is good advice. I was replying specifically to the OP's situation. I'd be surprised if the gravity had already stopped dropping at 5 days.

__________________
Tried to keep up with this signature, but just couldn't.